ARLINGTON, TEXAS - Baker Mayfield made his Heisman case and horrendous starts to each half doomed the TCU Horned Frogs in a blowout win for the Oklahoma Sooners in the Big 12 Championship Sunday.

TCU, the projected middle-of-the-pack finisher whose surprise season was fueled by an “eyes up, keep climbing” motto, did just that in the second quarter after falling in a 17-0 hole in the first.

A sensational touchdown catch by John Diarse and a 29-yard rainbow to Jalen Reagor had the Horned Frogs poised to challenge the Sooners and their FBS-best offense in the second half, down just 24-17 at the break.

But after an anticlimactic opening drive of the third, a 55-yard touchdown pass from Baker Mayfield to Mykel Jones proved to be the wind-out-of-the-sails moment.

There was no climbing after that for TCU.

Unlike the Sooners’ 38-20 win in Norman three weeks ago, a game in which Oklahoma visibly let off the gas pedal in the second half, OU stayed on the offensive Saturday at AT&T Stadium.

All Mayfield did was follow the aforementioned 55-yard score with a 52-yarder to Marquise Brown to put Oklahoma up 38-17. The two long touchdowns accounted for 44 percent of Mayfield’s 243 passing yards on the day.

"You can't give up big plays," TCU head coach Gary Patterson said. "...We gave up a couple. [...] Two plays is basically the second half.

"They turned up the volume and we did not."

Mayfield threw four touchdowns in the game and added 65 rushing yards -- 54 on one play -- en route to being named the Offensive MVP of the game.

The Heisman favorite's counterpart, TCU quarterback Kenny Hill, was stopped short of a first down on a fourth-down carry early in the third and threw an interception deep in TCU territory two possessions later.

The big win came after a historic start for OU, whose 17-0 lead at the end of the first quarter was the largest first-quarter lead in Big 12 Championship history.

"It really electrified this whole team," said Sooners tight end Mark Andrews, who caught seven passes including two touchdowns in the game. "It was big to get off to a start like that."

Oklahoma, which came into the game ranked third in the College Football Playoff rankings, will earn a berth in the four-team playoff for the second time in three years.

"I'll put the challenge out [to] whoever gets an opportunity to play them," Patterson said. "Have fun! We got a chance to do it twice."

Notes

• Oklahoma head coach Lincoln Riley is the first coach in Big 12 history to win the conference championship game in his first season as a head coach. Riley, just 34 years old, is the fifth coach in FBS history to win 12 games without any previous head coaching experience.

• Baker Mayfield has thrown at least two touchdowns in 26 straight games, tying Kellen Moore (2010-11 with Boise State) for the longest streak in FBS history.